1. Field of the Invention
The invention relates to a motor-driven machine with variable torque setting, in particular, a portable electric tool, comprising a motor and a planetary gearing driving a work spindle and including a rotatably mounted internal gear actuating a motor de-energizer against the action of a spring force when a settable limit torque is exceeded.
2. Description of the Related Art
Such motor-driven machines are known from German Patent 2 829 291. In the apparatus disclosed in this publication, the internal gear is provided on its end face with a cam element which rests against a ball which is spring-loaded in the direction of the end face of this internal gear. Once the opposing torque acting on the internal gear exceeds a certain limit value, the ball is displaced in the axial direction by the cam element and the motor de-energizer is actuated through this axial motion, which results in the motor being de-energized and hence the drive of the work spindle interrupted.
The above-described construction has the disadvantage that exact setting of the limit torque is not possible by the helical spring used therein. Also, the helical spring has the disadvantage that it does not permit a space-saving and compact apparatus design.
The object underlying the invention is, therefore, to so improve a machine with variable torque setting of the generic kind that it enables torque setting which is as precise as possible and a design which is as compact as possible.
This object is achieved, in accordance with the invention, in a motor-driven machine with variable torque setting of the kind described at the beginning by a torsion spring element extending in the axial direction along-side the planetary gearing being provided for generatin the spring force, the torsion spring element carrying at one end thereof a swivel element which engages a cam on the internal gear and being held at an opposite end in a support, by the swivel element being able to swivel out of an initial position against the action of the force of the torsion spring element, and by the motor de-energizer being thereby actuatable.
The great advantage of the invention solution is, above all, to be seen in the fact that a torsion spring element is used instead of a helical spring and that this torsion spring element extends longitudinally along an outer side of the planetary gearing and can thereby be implemented in a length which is adequate for a torque disconnection setting which is as exact as possible, without considerable additional space being required.
Use of a torsion element in connection with a gearing with a common countershaft is in fact known from German Offenlegungsschrift (unexamined Patent Application) 3 610 820 but in this apparatus the torsion element is arranged in front of the gearing parallel to the work spindle and, therefore, requires considerable additional space, which excludes a compact design.